More than 8% of the 2,513 respondents to the Stanford University phone survey said they hid their use from partners.

A typical addict is a single, white college-educated male in his 30s, who spends more than 30 hours a week on "non-essential" computer use, it found.

"We often focus on how wonderful the internet is; how simple and efficient it can make things," said Dr Elias Aboujaoude of the Stanford University School of Medicine and one of the researchers behind the study.

"But we need to consider the fact that it creates real problems for a subset of people."

Obsessive behaviour

Previous studies have shown that a significant number of people could be addicted to the internet.

For example, a 1999 Center for Internet Studies survey of 18,000 internet users found that 5.7% had signs of "compulsive" internet use.

Since then the internet has become quicker, richer in content and more accessible because of technology such as wireless.

The issue is starting to be recognized as a legitimate object of clinical attention

As a response, internet addiction clinics have sprung up around the world to try to wean people off their cyberspace fix. Last year, China opened its first clinic in Beijing

However, researchers say it is not clear whether compulsive internet use is a distinct problem or an expression of other underlying problems such as obsessive compulsive disorders.

The new study questioned 2,513 people in the US about their online habits.

The results showed that nearly 14% of respondents found it difficult to stay away from the internet for periods of several days.

Almost 6% said they felt their wanderings in cyberspace adversely affected their relationships with other people.

Nearly 8% of people said they went online to escape real world problems.

Behaviour like this, the researchers said, show similarities with other types of addictions such as alcoholism. Other parallels include hiding their online behaviour.

"The issue is starting to be recognized as a legitimate object of clinical attention, as well as an economic problem, given that a great deal of non-essential internet use takes place at work," said Dr Aboujaoude.

The research appears in the October edition of CNS Spectrums: The International Journal of Neuropsychiatric Medicine.